Valve is a Linux and Arch MVP, and as a die-hard Linux user, my appreciation for them is immense. Without Valve's efforts, Linux user base would be a lot smaller because a lot of people would be using Windows. I wouldn't be able to game (since I am a Linux-only house) without a complicated windows VM setup. So just the fact that they support Linux with their proprietary software, and the fact that they used Arch for the Steam Deck (giving strong commercial incentive to game devs to support linux or at least proton, which IMHO is good enough) is a big contribution to the community. They also made the Steam Deck fully hackable by the owners, so you can do neat things with it including running all your games from some other store if you want.

But on top of that, they contribute a ton of things that benefit even people who never touch Steam. Valve slings graphics stack and GPU code, and of course Proton/Wine, Gamescope, and a handful of other things. They are awesome about upstreaming stuff, and when it's not upstreamable (say for example a new or standalone project) they tend to open it.

Proton, Gamescope, Linux ESync/FSync Patches are all at least related to valves efforts from what I can gather and as an Arch User I feel it's the premier linux gaming distro due to valves efforts.

I think most of the work Valve does is upstream from Arch though but it's trickling down very fast (with arch, sometimes hours, if it's an AUR-Git package, seconds).